The prior art has continually sought refractory articles of improved strength for use in conventional steel making processes such as Basic Oxygen Furnace (BOF), Linz Donawitz (LD) and Quality Basic Oxygen Process (Q-BOP). Improvements of refractory articles in the prior art have been made by using magnesite of improved purity and density. For example, the use of magnesite containing low amounts of boron compounds or the adjustment of the silicate phase, so that low melting point minerals are not formed, has improved the high temperature strength of such articles.
Furthermore, the application of internal and/or external metal plates to refractory articles has demonstrated several advantages. The use of such plates is thought to provide a path of thermal conductivity through the article which acts to decrease the thermal gradient and accordingly to lower thermal stresses and reduce thermal shock. In addition, lowering the temperature of the hottest portions of the refractory article thereby reduces the rate of chemical attack. When the plates are used in bricks they also provide mechanical strengthening by joining the ends of the brick in the event of structural failure. The major disadvantage of using metal plates in refractory articles is that they seriously encumber the manufacturing process.
In general, long particles are known to provide a reinforcement network in ceramic articles and refractories which functions to transfer stress. Furthermore, from the science of fracture mechanics, it is known that crack propagation along a "tortuous path" requires higher energy to propagate the crack. Accordingly, refractory materials containing wire and other fibers have a higher fracture toughness.
In the prior art it is known to add fibers, particularly wire or metal fibers, to refractory articles to increase both the strength and service life of such articles. For example, one prior art method describes strengthening of refractory articles by using wires and other fibers in calcium aluminate cement-base refractory castables. Lankard and Sheets, Use of Steel Wire Fibers in Refractory Castables, 50 Bull Am. Ceramics Society No. 5 497 (1971).
Furthermore, it is well known in the art to add carbonaceous compounds to refractory compositions and articles. Such materials include coal tar pitch, tar or resins for the purpose of bonding aggregates or impregnating fired refractory brick with carbon. However, it has been discovered that the addition of a specific weight percentage of fibers to a refractory composition having a carbon-bearing matrix results in an unexpected, significant improvement of the service life of the composition or of a refractory article made from the composition. Apparently, this unexpected result is attributable to the fact that the carbon-bearing matrix protects the fibers chemically bonded thereto from oxidation. Therefore, because the strengthening fibers are effective for longer periods of time, refractory articles embodying them retain strength and utility for longer periods of time than non-carbonaceous refractory articles containing fibers.